Introduction: The confluence of biotechnology and nanotechnology has been an area of exciting research and profound technological advancement in the recent past. Bacterial cellulose (BC) is one of the widely known natural biopolymer nanofiber that can be classified as a natural nanobiomaterial. Its excellent physical properties, nanometer dimensions, high surface area, coupled with chemical properties such as poly-functionality and water holding capability can be exploited for a variety of biomedical applications[1],[2]. These include wound dressings[3], artificial blood vessels[4], scaffold material for tissue engineering of cartilage[5]. Control of wound infection is of principal importance in the clinical setting. Silver and silver based compounds have been a popular choice against microbial infection due to its effectiveness over a broad spectrum of pathogenic bacteria[6].
In the present study, we have investigated the surface functionalization of BC nanofibers and immobilization of nanocrystalline silver. The antimicrobial efficacy of silver loaded BC (BC-Ag) films has been demonstrated using Staphylococcous aureus and Eschericia coli, a Gram positive and Gram negative bacteria, respectively[7].
Materials and Methods: BC nanofibers were produced via fermentation using Gluconacetobacter xylinus (BPR 2001) bacterium using a procedure described previously[8]. Formation of BC-Ag was evidenced by SEM, FT-IR and Energy-dispersive X-ray spectroscopy. The silver content and release profile was quantified by atomic absorption spectrophotometer.
Results and Discussion: The presence of hydroxyl groups in cellulose allows various reactions possible with proper modification of cellulose. In this study, BC was oxidized using NaIO4 yielding dialdehyde cellulose. Then, thio groups were incorporated through a simple chiff’s base reaction which was followed by the two-step silver enhancement process. The uniform silver distribution along the length of the BC fibers were confirmed by SEM analysis. To confirm the positive identity of the particle as silver, EDX analysis was done (Fig.1.a and b).
Fig. 1. a) Back scattering, and b) EDX spectra of BC-Ag.
Furthermore, an EDX map of sulfur and silver on a sample of BC-Ag films positively identifies the association of silver nanoparticles to the BC backbone (Fig.2.a and b).
Fig. 2. Back scatter electron map of a) sulfur, and b) silver.
By tuning the reaction conditions we were able to tune the silver content of the resulting BC-Ag films from 2000 ppm to less than 500 ppm. The release profile of different BC-Ag films in simulated wound fluid was also investigated. The films displayed a sustained Ag+ release profile and films with higher silver content exhibited a higher and faster release profile.
The antibacterial activity of BC-Ag films at different times of oxidation were studied against agar plate cultures of the pathogenic bacteria E.coli (ATCC 29425) and S. aureus (ATCC 6538) using the clear zone test. The results demonstrated high antibacterial efficacy against both bacteria strains.
Conclusion: In summary, the fabrication BC-Ag was achieved and confirmed using different methods. Tuning the reaction conditions can precisely control the loading of silver nanoparticles and the release profile. BC-Ag films exhibited high antibacterial activity against E.coli and S.aureus strains and would find potential applications such as wound dressings.
References:
[1] Wu, J.; Zheng, Y.; Song, W.; Luan, J.; Wen, X.; Wu, Z.; Chen, X.; Wang, Q.; Guo, S., Carbohydrate Polymers 2014, 102, 762-771.
[2] Czaja, W.; Krystynowicz, A.; Bielecki, S.; Brown Jr, R. M., Biomaterials 2006, 27 (2), 145-151.
[3] Maneerung, T.; Tokura, S.; Rujiravanit, R., Carbohydrate Polymers 2008, 72 (1), 43-51.
[4] Andrade, F. K.; Costa, R.; Domingues, L.; Soares, R.; Gama, M., I Acta Biomaterialia 2010, 6 (10), 4034-4041.
[5] Lloyd, A., Materials Today 2004, 7 (11), 28.
[6] Sondi, I.; Salopek-Sondi, B., Journal of colloid and interface science 2004, 275 (1), 177-182.
[7] Wan, W. K., Guhados, G., US Patent Application 8,3667,089. 2013.
[8] Spaic, M.; Small, D.; Cook, J.; Wan, W., Cellulose 2014, 21 (3), 1529-1540.